Pixel Element of Liquid Crystal Display and Method for Producing the Same

ABSTRACT

The present invention provides a method for forming a pixel element. The method comprises: forming a first patterned metal layer within the pixel area; forming an insulation layer on the first patterned metal layer; forming a semiconductor layer on the insulation layer; patterning the semiconductor layer to form bend seed generation portion; and forming a second metal layer to connect the semiconductor layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates Liquid Crystal Display, and moreparticularly, to pixel element of Liquid Crystal Display.

2. Description of the Prior Art

The Liquid Crystal Display can be classified according to kinds of theliquid crystal, kinds of driving method, kinds of light source, and thelike. One type of the Liquid Crystal Display—Optically CompensatedBirefringence Liquid Crystal Display or Optically Compensated BendLiquid Crystal Display, OCB LCD—has a quick response time so that it canprovide fluent visions to the viewer.

Before normal operation, the liquid crystal molecules of the OCB LCDmust be transformed from the splay state to the bend state. FIG. 1A andFIG. 1B respectively illustrate the splay state and bend state of theliquid crystal molecules of the OCB LCD, wherein FIG. 1A shows the splaystate, and FIG. 1B shows the bend state.

As shown in FIGS. 1A and 1B, an OCB LCD 10 comprises a liquid crystallayer 11 arranged between a thin-film transistor substrate 13 and acolor filter substrate 12. Before an electrical field is applied to theliquid crystal layer 11, the liquid crystal molecules of the liquidcrystal layer 11 is arranged at splay state. When an electrical filed isapplied to the liquid crystal layer 11, the liquid crystal molecules ofthe liquid crystal layer 11 are transformed to the bend state. Thistransformation process is typically called as “start up” procedure. TheOCB LCD cannot be normally operated until the “start up” procedure iscompleted. A conventional OCB LCD typically needs several minutes forcarrying out the start up procedure, and always the user is impatient towait.

As shown in FIG. 2, U.S. Pat. No. 6,597,424 discloses a pixel element ofan OCB LCD to speed the start up procedure. Data lines 21 and gate lines22 define a pixel element, which comprises a pixel electrode 24 and aswitch transistor 23 for driving the pixel electrode 24, where the pixelelectrode 24 has recess portions 25 a and protrusion portions 25 b atthe neighborhood of its edges, and the data lines 21 and gate lines 22have corresponding protrusion portions 26 a/27 a and recess portions 26b/27 b. Some potential differences are applied between the pixelelectrode 24 and the data lines 21 and between the pixel electrode 24and the gate lines 22, thereby forming a transverse electric field togenerate bend seeds that can help the transformation of the state of theliquid crystal layers, so that the start up procedure can beaccelerated.

Although the above pixel element can speed the start up procedure, theaperture ratio is inevitably decreased. Because the shape of theprotrusion portions 25 b/26 a/27 a and the recess portions 25 a/26 b/27b are irregular, it is needed to be covered by a black matrix having thesame irregular shape but a more large area, and therefore the apertureratio is decreased.

Therefore, it would be advantageous to provide a pixel element and amethod for producing the pixel element, which the start up procedure canbe speeded and an excellent aperture ratio can be maintained.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a pixel element ofLiquid Crystal Display and its forming method, which can speed up thestart up procedure, and maintain the aperture ratio of the LiquidCrystal Display.

According to the object, the present invention provides a method forforming a pixel element of a Liquid Crystal Display, comprising: forminga patterned first electrode layer within the pixel area of the LiquidCrystal Display; forming an insulation layer on the patterned firstelectrode layer; forming a semiconductor layer on the insulation layer;patterning the semiconductor layer to form a bend seed generationportion; and forming a patterned second electrode layer to connect thesemiconductor layer.

According to the object, the present invention provides a pixel elementof a Liquid Crystal Display, the Liquid Crystal Display comprising apixel array defined by a plurality of data lines and a plurality of gatelines, each of the pixel element of the pixel array comprising: a gateline or a common line on a thin-film transistor substrate; an insulationlayer on the gate line or the common line; a semiconductor layer havinga plurality of bend seed generation portions on the insulation layer;and a data line on the semiconductor layer, the data line connecting tothe semiconductor layer.

According to the object, the present invention provides a pixel elementof a Liquid Crystal Display, the Liquid Crystal Display comprising apixel array defined by a plurality of data lines and a plurality of gatelines, each of the pixel element of the pixel array comprising: a gateline or a common line on a thin-film transistor substrate; an insulationlayer on the gate line or the common line; a semiconductor layer havinga plurality of bend seed generation portions on the insulation layer;and a second electrode layer on the semiconductor layer, the secondelectrode layer connecting to the semiconductor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B show two states of liquid crystal molecules of aconventional OCB.

FIG. 2 is a diagram of a pixel element according to a conventional OCB.

FIG. 3 and FIG. 4 show a method for forming a pixel element according toone embodiment of the present invention.

FIGS. 5A, 5B, 5C, 6, and 7 show a pixel element and its variationaccording to embodiments of the present invention.

FIGS. 8A, 8B, 8C, 8D, 9A, 9B, 10A, and 10B show a pixel element and itsvariation according to other embodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The detailed description of the present invention will be discussed inthe following embodiments, which are not intended to limit the scope ofthe present invention, but can be adapted for other applications. Whiledrawings are illustrated in details, it is appreciated that the quantityof the disclosed components may be greater or less than that disclosed,except expressly restricting the amount of the components. Whereverpossible, the same or similar reference numbers are used in drawings andthe description to refer to the same or like parts. It should be notedthat any drawings presented are in simplified form and are not toprecise scale. In reference to the disclosure herein, for purposes ofconvenience and clarity only, directional terms, such as, top, bottom,left, right, up, down, over, above, below, beneath, rear, and front, areused with respect to the accompanying drawing. Such directional termsshould not be construed to limit the scope of the invention in anymanner.

The key to speed the start up procedure of the prior art is to generatebend seeds by altering the essential configuration of the pixel element,but the altered pixel element sacrifices the aperture ratio andcomplicates the manufacturing process. In view of the defects of theprior art, the present invention provides a pixel element and a methodfor producing the pixel element that can speed the start up procedure onconditions that the essential configuration of the pixel element is notaltered, the manufacturing process is not complicated, and the apertureratio can be maintained as before.

FIG. 3 shows a forming method of a pixel element according to oneembodiment of the present invention. Step 31, a patterned firstelectrode layer is formed within the pixel area, where the firstelectrode layer and the gate lines can be formed in the same layer; or,the first electrode layer comprises a gate line or a common line (alsoreferred to as bias line in the pixel element of Liquid CrystalDisplay). In this text, gate lines and data lines define the pixel areathat comprises a central region and a boundary region. Generally twodata lines and two gate lines define one (or more) pixel, and the firstelectrode layer may be formed at the central region and/or the boundaryregion. Step 32, an insulation layer is formed on the patterned firstelectrode layer. Step 33, a semiconductor layer is formed on theinsulation layer. The semiconductor layer may be made from a materialchosen from the group consisting of polycrystalline silicon,microcrystalline silicon, amorphous silicon, and combination thereof.Step 34, the semiconductor layer is patterned to form a plurality ofbend seed generation portions. Step 35, a patterned second electrodelayer is formed to connect the semiconductor layer. In one embodiment,the second electrode layer and the data lines are formed at the samelayer and the second electrode layer is connected to at least one of thedata lines, or, the second electrode layer comprises a data line or acapacitor electrode. In another embodiment, the second electrode layercomprises a pixel electrode, and a passivated layer is arranged betweenthe pixel electrode and the semiconductor layer. The pixel electrodeconnects the semiconductor layer via at least a contact hole. It isappreciated that at least a portion or the whole of the semiconductorlayer is right on the first electrode layer according to the presentinvention.

FIG. 4 shows a driving method applied to the pixel element produced bythe method of FIG. 3 for accelerating the start up procedure. Step 41, afirst positive voltage is applied to the first electrode layer. Step 42,a plurality of electrons having a polarity opposite to the firstpositive voltage are aggregated in the bottom of the semiconductor layerdue to the exertion of the first positive voltage. Step 43, a secondpositive voltage is applied to the second electrode layer, wherein thefirst positive voltage is greater than the second positive voltage. Step44, the electrical potential of the semiconductor layer equalizes theelectrical potential of the second electrode layer, because thesemiconductor layer now works as an electrical conductor. Step 45, bendseeds are generated from bend seed generation portions of thesemiconductor layer due to the transverse electric field caused by thepotential difference between the first electrode layer and thesemiconductor layer.

In the above method, the performance of the semiconductor may be changedby at least one additional implanting process, which forms at least onedoped region. For example, forming a N+ heavily doped region in thesemiconductor layer may form an Ohmic contact between the semiconductorlayer and the second electrode layer. In addition, the first positivevoltage and/or the second positive voltage may be changed to a firstnegative voltage and/or a second negative voltage on a condition thatthe potential difference is sufficient to generate the bend seeds.Further, because the start up procedure differs from the normaloperation, the voltages applied to the first and second electrode layerduring the start up procedure may be different from the voltages appliedto the first and second electrode layer during the normal operation. Forexample, if the first electrode layer comprises a gate line and thesecond electrode layer comprises a data line, then a voltage 10V to 15Vmay be applied to the gate line and a voltage 0 to 10V may be applied tothe data line during the normal operation, and a voltage 40V may beapplied to the gate line and a voltage 0 to 1V may be applied to thedata line during the start up operation.

FIG. 5A to FIG. 5C show a pixel element according to one embodiment ofthe present invention, wherein FIG. 5B is a part enlarged view of FIG.5A, FIG. 5C is a cross-sectional view of FIG. 5A taken along a lineX-X′.

In the embodiment of FIG. 5A, two gate lines 51 and two data lines 52define a pixel element 50, but this should not be limited. As mentionedabove, a semiconductor layer 54/55 having bend seed generation portionsmay be formed in the boundary region of the pixel element. For example,a semiconductor layer 54 is formed between a common line 53 and a dataline 52, or, a semiconductor layer 55 is formed between a gate line 51and the data line 52. The pixel element 50 further comprises a pixelelectrode 56 for driving the liquid crystal molecules and a thin-filmtransistor 57 for controlling the pixel electrode 56. The structure ofthe thin-film transistor 57 may be same as the structure of the priorart, which comprises a gate, a source, and a drain, or, the thin-filmtransistor 57 may be other type of switch elements. In addition, thepixel element 50 comprises a capacitor electrode 58, wherein thecapacitor electrode 58 and the common line 53 construct a storagecapacitor formed on the common line (typically called “Cst on common”).In other embodiments of the present invention, the storage capacitor ofthe pixel element 50 may be formed on the gate line (typically called“Cst on gate”).

FIG. 5B illustrate the geometry of the semiconductor layer according toone embodiment of the present invention. For forming bend seedgeneration portions, the semiconductor layer 54 is hollowed to form atleast one polygon-shaped opening. As shown in FIG. 5B, the eightdouble-arrow lines within the opening shown will be the bend seedgeneration portions. It is appreciated that the outline of thepolygon-shaped may comprises obtuse angle, acute angle, right angle, andother irregular shapes. In addition, the different positions of thesemiconductor layer may comprise the same or different shape of the bendseed generation portions. For example, the semiconductor layer 55 mayhas a shape different from (or same with) the shape of the semiconductorlayer 54.

FIG. 5C is a cross-sectional view taken along the line X-X′ of FIG. 5A.As shown in FIG. 5C, the common line 53 is formed on the substrate 59,the insulation layer 60 is formed on the common line 53, thesemiconductor layer 54 having bend seed generation portions is formed onthe insulation layer 60, and the data line 52 is formed on thesemiconductor layer 54.

FIG. 6 and FIG. 7 illustrate two semiconductor layers having differentshapes according to two embodiments of the present invention. Forconvenience, the same reference numbers are used in later embodiments torefer to the same elements mentioned before, and the same description ofwhich are omitted. Referring to FIG. 6, the semiconductor layer 54comprises at least one protrusion portion 61 as the bend seed generationportion. Referring to FIG. 7, the semiconductor layer 54 is hollowed toform at least one polygon-shaped opening, where the outline of theopening comprises obtuse angle, acute angle, right angle, and otherirregular shapes, the outer outline of the semiconductor layer 54comprises at least one protrusion portion, and all of these un-smoothshapes will function as the bend seed generation portions.

FIG. 8A to FIG. 8D illustrate that the semiconductor layer having bendseed generation portions may be formed in the storage capacitor of thepixel element, wherein FIG. 8B is a part enlarged view of FIG. 8A, andFIG. 8C is a cross-sectional view taken along a line Y-Y′ of FIG. 8A.

Referring to FIG. 8A and FIG. 8B, the semiconductor layer 62 is arrangedunder the capacitor electrode 58, and the semiconductor layer 62comprises protrusion portions 67 as the bend seed generation portions.The capacitor electrode 58 connects with pixel electrode 56 via thecontact hole 63, so that the electrical potential of the capacitorelectrode 58 equals the electrical potential of the pixel electrode 56.

Referring to FIG. 8C, which is a cross-sectional view taken along theline Y-Y′ of FIG. 8A. The common line 53 is formed on a substrate 59,the insulation layer 60 is formed on the common line 53, thesemiconductor layer 62 having bend seed generation portions is formed onthe insulation layer 60, the capacitor electrode 58 is formed on thesemiconductor layer 62, a passivated layer 64 is formed on the capacitorelectrode 58, and a pixel electrode 56 is formed on the passivated layer64 and is connected with the capacitor electrode 58 via a contact hole63.

The semiconductor layer 62 of FIG. 8C is formed within a “MIM”(Metal/Insulation/Metal) type of storage capacitor, where the commonline 53 and capacitor electrode 58 as two electrodes of the storagecapacitor, and the semiconductor layer 62 having bend seed generationportions is formed under the capacitor electrode 58. FIG. 8D showsanother embodiment of the present invention in which the capacitorelectrode 58 is omitted, and the pixel electrode 56 functions as anotherelectrode of the storage capacitor and connects with the semiconductorlayer 62 via the contact hole 63.

FIG. 9A and FIG. 9B illustrate the geometry of the semiconductor layeraccording to another embodiment of the present invention, wherein FIG.9B is a part enlarged view of FIG. 9A. The semiconductor layer 65 ishollowed to form at least one polygon-shaped opening, where the outlineof the opening comprises obtuse angle, acute angle, right angle, andother irregular shapes as bend seed generation portions.

FIG. 10A and FIG. 10B illustrate the geometry of the semiconductor layeraccording to another embodiment of the present invention, wherein FIG.10B is a part enlarged view of FIG. 10A. The semiconductor layer 66 ishollowed to form at least one polygon-shaped opening, where the outlineof the opening may comprise obtuse angle, acute angle, right angle, andother irregular shapes, the outer outline of the semiconductor layer 54comprises at least one protrusion portion, and all of these un-smoothshapes will function as the bend seed generation portions.

The above-mentioned embodiments illustrate variant geometry of thesemiconductor layer, but it is should not be limited by the drawings. Inaddition, the geometry of FIG. 8A to FIG. 10B may be applied in astorage capacitor that is formed on the gate (typically called “Cst ongate”). The only difference compared with the Cst on gate structure isthat the gate line will be another reference electrode instead of thecommon line; therefore the description and drawings are omitted forsimplicity and clarity.

The method of FIG. 4 can be applied to all above-mentioned embodimentsof the present invention; the only difference between embodiments isthat the first electrode layer and the second electrode layer may bedifferent and they may connect to different elements so that they havedifferent electrical potentials. For embodiment of FIG. 5C, the firstelectrode layer corresponds to the common line, the second electrodelayer corresponds to the data line, and the electrical potential of thedata line equals the electrical potential of the semiconductor layer;for embodiment of FIG. 8C, the first electrode layer corresponds to thecommon line, the second electrode layer corresponds to the capacitorelectrode, and the electrical potential of the pixel electrode equalsthe electrical potential of the capacitor electrode and the electricalpotential of the semiconductor layer; for embodiment of FIG. 8D, thefirst electrode layer corresponds to the common line, the secondelectrode layer corresponds to pixel electrode, and the electricalpotential of the pixel electrode equals to the electrical potential ofthe semiconductor layer via the contact hole.

The pixel element and the method for producing the pixel elementaccording to the present invention can be applied to a Liquid CrystalDisplay, which comprises a thin-film transistor substrate and a colorfilter substrate, wherein the pixel element is arranged within thethin-film transistor substrate. The color filter substrate comprises acommon electrode. An electrical field is applied between the commonelectrode and the pixel electrode of the thin-film transistor substratefor driving the liquid crystal molecules between two substrates.According to the pixel element and its forming method of the presentinvention, the potential difference between the first electrode layerand the second electrode layer generates transverse electrical filed, sothat the bend seed generation portions of the semiconductor layergenerate a plurality of bend seeds, and by an electrical field appliedbetween the two substrates, the bend seeds help the all liquid crystalmolecules to be transformed completely, thereby speeding up the start upprocedure. The experiment results show that the start up procedure ofthe OCB LCD of the present invention can be completed less than 3seconds, even less than 1 second.

According to the pixel element and its forming method of the presentinvention, the pixel electrode is needless to be altered, and becausethe area of the bend seed generation portions is quite small, theaperture ratio is almost unchanged. In addition, the method of producingthe pixel element of the application is compliant with currentmanufacturing method. For example, the step 33 for forming asemiconductor layer on the insulation layer is the same step for forminga semiconductor layer of the thin-film transistor, so that no anyfurther step is needed. Accordingly, the pixel element and its producingmethod of the present invention is indeed an excellent solution forspeeding up the start up procedure.

Although specific embodiments have been illustrated and described, itwill be appreciated by those skilled in the art that variousmodifications may be made without departing from the scope of thepresent invention, which is intended to be limited solely by theappended claims.

1. A method for forming a pixel element of a Liquid Crystal Display,comprising: forming a patterned first electrode layer within the pixelarea of said pixel element; forming an insulation layer on saidpatterned first electrode layer; forming a semiconductor layer on saidinsulation layer; patterning said semiconductor layer to form a bendseed generation portion; and forming a patterned second electrode layerto connect said semiconductor layer.
 2. The method as recited in claim1, further comprising: applying a first voltage to said first electrodelayer; aggregating a plurality of electrons or electron holes in thebottom of said semiconductor layer depending on the polarity of saidfirst voltage, said plurality of electrons or electron holes have apolarity opposite to the polarity of said first voltage; applying asecond voltage to said second electrode layer, wherein the electricalpotential of said first voltage is greater or smaller than theelectrical potential of the second voltage; equalizing the electricalpotential of said semiconductor layer and the electrical potential ofsaid second electrode layer; and generating bend seeds from said bendseed generation portion of said semiconductor layer due to a transverseelectrical field caused by the potential difference between said firstelectrode layer and said semiconductor layer.
 3. The method as recitedin claim 1, wherein said first electrode layer comprises a gate line. 4.The method as recited in claim 1, wherein said first electrode layercomprises a common line.
 5. The method as recited in claim 1, whereinsaid second electrode layer and a data line are formed at a same layer,and said second electrode layer connects with the data line.
 6. Themethod as recited in claim 1, wherein said second electrode layercomprise a data line.
 7. The method as recited in claim 1, wherein saidsecond electrode layer comprises a capacitor electrode of a storagecapacitor.
 8. The method as recited in claim 1, wherein said secondelectrode layer comprises a pixel electrode, a passivated layer isarranged between said pixel electrode and said semiconductor layer, andsaid pixel electrode connects with said semiconductor layer via acontact hole.
 9. The method as recited in claim 1, wherein saidsemiconductor layer is made of a material chosen from the groupconsisting of polycrystalline silicon, microcrystalline silicon,amorphous silicon, and combination thereof.
 10. The method as recited inclaim 1, further comprising at least one implanting process for formingat least one doped region, thereby forming an Ohmic contact between saidsemiconductor layer and said second electrode layer.
 11. The method asrecited in claim 1, wherein at least a portion of said semiconductorlayer is right on said first electrode layer.
 12. A pixel element of aLiquid Crystal Display, said Liquid Crystal Display comprising a pixelarray defined by a plurality of data lines and a plurality of gatelines, each of said pixel element of said pixel array comprising: a gateline or a common line on a thin-film transistor substrate; an insulationlayer on said gate line or said common line; a semiconductor layerhaving a plurality of bend seed generation portions on said insulationlayer; and a data line on said semiconductor layer, said data lineconnecting to said semiconductor layer.
 13. The pixel element as recitedin claim 12, wherein a first voltage is applied to said gate line orsaid common line, a second voltage is applied to said data line, thepotential difference between the first voltage and the second voltagegenerates a transverse electrical field, and bend seeds are generatedfrom said bend seed generation portions of said semiconductor layer. 14.The pixel element as recited in claim 12, wherein said semiconductorlayer is hollowed to form at least one polygon-shaped opening, and theoutline of the polygon-shaped opening comprises obtuse angle, acuteangle, right angle, or other irregular shapes as said bend seedgeneration portion.
 15. The pixel element as recited in claim 12,wherein the outer outline of said semiconductor layer comprises at leastone protrusion portion as the bend seed generation portion.
 16. Thepixel element as recited in claim 12, wherein said semiconductor layeris hollowed to form at least one polygon-shaped opening, the outline ofthe opening comprises obtuse angle, acute angle, right angle, or otherirregular shapes as the bend seed generation portion, and the outeroutline of said semiconductor layer comprises at least one protrusionportion as the bend seed generation portion.
 17. The pixel element asrecited in claim 12, wherein at least a portion of said semiconductorlayer is right on said first electrode layer.
 18. A pixel element of aLiquid Crystal Display, said Liquid Crystal Display comprising a pixelarray defined by a plurality of data lines and a plurality of gatelines, each of said pixel element of said pixel array comprising: a gateline or a common line on a thin-film transistor substrate; an insulationlayer on said gate line or said common line; a semiconductor layerhaving a plurality of bend seed generation portions on said insulationlayer; and a second electrode layer on said semiconductor layer, saidsecond electrode layer connecting to said semiconductor layer.
 19. Thepixel element as recited in claim 18, wherein said second electrodelayer comprises a capacitor electrode, and further comprises apassivated layer on said capacitor electrode and a pixel electrode onsaid passivated layer, said pixel electrode connecting with saidcapacitor electrode via a contact hole.
 20. The pixel element as recitedin claim 18, wherein said second electrode layer comprises a pixelelectrode, and further comprises a passiveted layer between saidsemiconductor layer and said pixel electrode, said pixel electrodeconnecting with said semiconductor layer via a contact hole.
 21. Thepixel element as recited in claim 18, wherein a first voltage is appliedto said gate line or said common line, a second voltage is applied tosaid second electrode layer, the potential difference between the firstvoltage and the second voltage generates a transverse electrical field,and bend seeds are generated from said bend seed generation portion ofsaid semiconductor layer.
 22. The pixel element as recited in claim 18,wherein said semiconductor layer is hollowed to form at least onepolygon-shaped opening, and the outline of the polygon-shaped openingcomprises obtuse angle, acute angle, right angle, or other irregularshapes as said bend seed generation portion.
 23. The pixel element asrecited in claim 18, wherein the outer outline of said semiconductorlayer comprises at least one protrusion portion as the bend seedgeneration portion.
 24. The pixel element as recited in claim 18,wherein said semiconductor layer is hollowed to form at least onepolygon-shaped opening, the outline of the opening comprises obtuseangle, acute angle, right angle, or other irregular shapes as the bendseed generation portion, and the outer outline of said semiconductorlayer comprises at least one protrusion portion as the bend seedgeneration portion.
 25. The pixel element as recited in claim 18,wherein at least a portion of said semiconductor layer is right on saidfirst electrode layer